The present invention relates to a multi-functional sensor with a single sensing element which corresponds to the amounts of water vapor and other gases in the surrounding atmosphere with a higher degree of sensitivity and which can detect the humidity and the concentration of reducing gases in the surrounding atmosphere in terms of variations in electrical resistance across the sensing element.
So far special sensors have been used to sense or detect the humidity and the presence of gases in the surrounding atmosphere. For instance, humidity sensing elements have been used exclusively in conjunction with humidity measuring instruments and humidity controlling systems and gas sensing elements have been used exclusively in conjunction with instruments for gas concentration and gas leakage alarming systems.
However, there has not yet been devised and demonstrated a single sensing element which is capable of sensing both the humidity and the gas content in the surrounding atmosphere with a reliable degree of accuracy. The reason why it had been difficult to develop such multi-functional sensors becomes apparent when one considers the use of a multi-functional sensor in an automatic control system for cooking equipment such as microwave ovens. The sensing element would be exposed not only to the water vapor but also the air containing various gases and oils. Some sensing elements would undergo chemical reactions with the gases and, or oils in the air, and the gases and oils would adhere to the surfaces of the sensing element, so that sensitivity would be degraded considerably. Another reason is that the sensing elements which have been used in practice and are made of n-type tin or iron oxides cannot detect both the humidity and the gas content in the surrounding atmosphere with a satisfactory degree of accuracy.